Sea Level- Number and Size of Continents

• Pangaea: “supercontinent” that existed 260-240 million years ago

• supercontinents have less coastlines, more harsh continental interiors

  • supercontinents: each of several large landmasses thought to have divided to form the present continents in the geologic past

    • the large landmasses were Gondwana, Pangaea, and Laurasia

• lower species diversity

• extinctions can occur when supercontinents are formed

  • different species on separate continents are forced to compete for food and habitats

Sea Level- Seafloor Spreading Rates

• new oceanic crust is created at divergent boundaries

• the amount of magma that rises and creates new crust at these boundaries changes over geologic time

• more magma = rapid spreading, more mass and volume of new, hot and buoyant rock

  • elevation of seafloor is raised

  • volume of space in ocean basins to hold water is reduced

  • sea level rises

Example: Seafloor Spreading in the Cretaceous

• 110-85 million years ago

• much faster spreading, so there is a lot of new oceanic crust

• global seas level> 660 feet higher than today

• shallow seas covered continents like North America

• the world climate was much warmer than it is today

• the rate of extinction of land-animal species increased